First congrats on adding on and updating the most valuable room of a home. Knowing foster City I will assume you did it with permit. It is very difficult ot put a value on an updated kitchen. They are all done differently. Here is a quick reference. http://www.pruvoices.com/2010/05/remodeling-dont-do-it-to-re
The return might be different when you are ready to go to market. Several years ago almost all updating got the cost back and more. Now paint and flooring are about the only two guarantees. An updated kitchen in any market it makes your home sell considerably faster and that in it;'s self money.
Your home being 200 sq. ft smaller is not a major concern. The floor plan is more important.
If you want give me your address and I will check what the county records shows for your home. No cost and no obligation.
NOt sure where you found out your neighbors home sold for $1,300,000 but sometiems the published sales price can be misleading. The factors that will affect the real value are the termite report, owner financing, seller credits to the buyer, rentbacks, etc. A good real estate agent can track down most of that info for you.
Good Luck but remember markets change and marketing activities need to change with that.
Sorry for your bad experience.
Let me answer the easy question first:
"...who do we get to do an actual measurement of the existing home?"
It's quite simple to pull your own measurements using the outside walls (the garage should not be included as part of the living space). Additionally, an Appraiser will always gather the physical living space square footage of a home. However, neither of these options may be necessary as the plans that you used for obtaining your building permits (I sure hope you obtained permits!) should list this. Note: If you did not obtain permits an Appraiser will not be able to assign value to your improvements.
Regarding the question of value:
Specifics are important when determining current estimated value. An individual should never use median or average statistical values for making a financial decision. All of the specifics of your home have not been shared, which makes arriving at reasonable valuation difficult. Given this, and assuming it's important for you to know current value, I would suggest you seek out a Realtor to perform a Comparative Market Analysis (CMA). A CMA always provides the best representation of market price/activity/trend direction - for the SPECIFIC property details you search on.
Updating and adding square footage to a kitchen is one of the best investments a homeowner can do and you will see a good return on that work.
You could easily check the county records to see what they show regarding the square footage and then add the additional 250sq.ft to that. That does not cost you anything and will give you a quick figure.
Otherwise to have a person come out and measure will be an expense.
Let me know if I can be of any further help.
It sounds like you need an appraiser if you want to know the sq ft of your home. If you need a referral, I have a good one who will not charge you that much if all you need is to find out the size of your home.